Not Applicable
Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates generally to poppet valves for internal combustion engines, and more particularly to a method of making a seat faced engine poppet valve.
2. Description of the Related Art
It is well known in the industry that engine poppet valves, particularly exhaust valves for heavy and moderate duty applications like those found in diesel and leaded fuel engine applications, operate at relatively high temperatures and in somewhat corrosive environments. In the manufacture of engine poppet valves, it is a common practice to face the valve with a corrosion, wear, abrasion, and heat resistant alloy to protect the valve face and enhance the useful life of the valve. The term xe2x80x9cfacingxe2x80x9d, or xe2x80x9cseat facingxe2x80x9d as used herein is intended to encompass the term xe2x80x9chard facingxe2x80x9d which is also used in the industry. These terms refer to providing the valve face with a corrosion, wear, abrasion, and/or heat resistant alloy to attain the necessary wear and corrosion resistance required for the given application. There is continued interest in seat facing poppet valves, both intake and exhaust valves, for high performance engines as well as smaller engines for use in motorcycles, for example.
Typically, the facing material has been a cobalt based alloy such as a Stellite(copyright) alloy (Stellite is a registered trademark of Deloro Stellite Company, Inc.), or a nickel based alloy like Eatonite(copyright), (Eatonite is a registered trademark of Eaton Corporation). More recently, Eatonite(copyright) 6, an iron based alloy, has been used and is rapidly replacing cobalt based alloys. There are other alloys for seat facing, including but not limited to, nickel-chromium, or nickel-chromium-cobalt base alloys, or various alloys known in the industry. The facing is usually applied to the valve seating surface by various high temperature techniques, like welding. The seat facing is preferably applied in a manner that can control metallurgy and microstructure. Typical heat sources for welding include, but are not limited to, oxy-acetylene torch, tungsten inert gas arc (TIG), or plasma arc (transferred or non-transferred), or the like.
The plasma transferred arc process offers several advantages over flame welding processes including but not limited to: precision controllable heat source and lower energy consumption which can provide finer microstructure and narrower heat affected zones (HAZ); versatility for powders and different raw materials; higher volume production capability; and minimum raw material waste. However, the current plasma transferred (PTA) process operates at such a high temperature that in some valve applications the torch burns through the valve from the seat facing groove to the valve combustion face on the valve head. An obvious solution to this problem is to simply add additional stock material to the combustion face to act as a heat sink. However, that option adds to the cost of manufacturing due to the extra machining required to remove the material afterwards as well as the cost of the material itself, as a waste material.
Consequently, there still exists a need for an improved process of seat facing an engine poppet valve which addresses the aforementioned problem of xe2x80x9cburn-throughxe2x80x9d as well as others, and particularly this problem with seat facing small poppet valves intended for use in high performance engines like those employed in small internal combustion motors such as motorcycle engines. Preferably, the method would avoid PTA burn-through of the valve head and reduce or even eliminate any unnecessary machining operations for removing excess material.
Accordingly, an object of the present invention is to provide an improved method for making an engine poppet valve that prevents burn-through during the seat facing step.
Another object of the present invention is to provide an improved method for making a small engine poppet valve.
Still another object of the present invention is to provide an improved process for making an engine poppet valve that reduces the number of machining steps.
Still another object of the present invention is to provide an improved method for seat facing engine poppet valves using a plasma transferred arc welding process.
A further object of the present invention is to provide an improved method for making engine poppet valves that is cost effective and reduces waste material.
In the method for making an engine poppet valve in accordance with the present invention, the method comprises the steps of forging an unfinished poppet valve from stock material to provide a valve head having an initial head diameter; forming a seat facing groove in the valve head of the unfinished poppet valve; providing an initial thickness of an interface of the seat facing groove and a combustion face of the unfinished poppet valve; depositing seat facing material in the seat facing groove; and reheating the valve head and coining a desired head diameter while hot forming the seat facing material into the interface to decrease the interface from the initial thickness to a final thickness, and increase the valve head diameter from the initial diameter to the desired diameter for finishing the engine poppet valve.
In another aspect, the present invention is directed to the engine poppet valve manufactured in accordance with the process of the present invention.
The various features of novelty, which characterize the invention, are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is described and illustrated.